This invention relates to water-absorbent film constructions. More particularly, this invention relates to a water-absorbent film construction comprising a water-absorbent film layer overlying a base layer, the water-absorbent film layer being comprised of at least about 40% by weight of a 2-oxazoline polymer.
Polymers of 2-oxazolines are known to be hydrophilic water-soluble materials. These polymers have utility as adhesion promoters and viscosity modifiers. Unfortunately, however, these polymers when formed into solid articles such as films exhibit poor mechanical properties. For example, dried films of 2-oxazoline polymers are too brittle to be useful in many applications and water often causes dissolution of such films.
Despite mechanical problems which limit the utility of these polymers, 2-oxazoline polymers have many desirable properties and it would be advantageous if they could be utilized in a film construction. The problem therefore is to pprovide a film construction containing a 2-oxazoline polymer that takes advantage of the desirable properties of this polymer and yet exhibits sufficient mechanical and physical properties to be of practical use. This problem has been overcome with the present invention.
U.S. Pat. No. 4,678,833 discloses miscible blends of poly-2-oxazolines and thermoplastic polymers. These blends are described as being useful as membranes for separating components of liquid mixtures such as water/ethanol or ethanol/hexane mixtures.
This invention relates to a water-absorbent film construction, comprising: a water-absorbent film layer overlying a base layer, the water-absorbent film layer being comprised of at least about 40% by weight of at least one 2-oxazoline polymer.
In one embodiment of the invention, the base layer has a first side and a second side, the water-absorbent film layer overlies the first side, and a skin layer overlies the second side.
In one embodiment of the invention, the inventive film construction further comprises a tie layer positioned between the water-absorbent film layer and the base layer.
In one embodiment of the invention, the base layer has a first side and a second side, the water-absorbent film layer overlies the first side, a tie layer is positioned between the water-absorbent film layer and the base layer, and a skin layer overlies the second side.
In one embodiment of the invention, the base layer has a first side and a second side, the water-absorbent film layer overlies the first side, a skin layer overlies the second side, and an adhesive layer overlies the skin layer. In one embodiment, the adhesive layer is comprised of a pressure sensitive adhesive, and a release liner overlies the pressure sensitive adhesive.
In one embodiment, the invention relates to a water-absorbent film construction, comprising: a water-absorbent film layer having a 2-oxazoline polymer concentration of at least about 40% by weight; a base layer, the base layer having a first side and a second side, the water-absorbent film layer overlying the first side of the base layer; and a skin layer comprising at least one heat-activatable adhesive material overlying the second side of the base layer.
In one embodiment, the invention relates to a write-on sheet protector, comprising: an envelope having an outer surface and an inner surface and being formed of a transparent coextruded sheet material; the sheet material comprising a water-absorbent film layer having a 2-oxazoline polymer concentration of at least about 40% by weight, a base layer, the base layer having a first side and a second side, the water-absorbent film layer overlying the first side of the base layer, and a skin layer overlying the second side of the base layer; the skin layer forming the inner surface of the envelope; the water-absorbent film layer forming the outer surface of the envelope; the other surface of the envelope being an ink receptive surface.